What to do if space for database decrease and no additional harddrive is possible?

Hi there.

I have a huge database with several tables. Some tables have statistics
information. And it's very huge. I don't want to loose any of this data.
But hard drives on my single server are not eternal. Very soon, there will
be no left space. And the most awful this, that it's a 1U server, and I
can't install new hard drive.

What can I do to enlarge space, without loosing data and performance?

Thanks for patience.